Phosphorus-containing metal oxide catalysts are used in various reactions, such as oxidation, oxidative dehydrogenation or ammoxidation of organic compounds, and dehydration, hydration or dehydrogenation of organic compounds. In some of these catalyst systems, a phosphorus component is present in a relatively small proportion to act like a promoter, and in others it is present in a major proportion in the form of a solid phosphoric acid or a phosphate.
Examples of the use of phosphorus-containing metal oxide catalysts include production of acrolein by oxidation of propylene (JP-B-36-3563) (the term "JP-B" as used herein means "an examined Japanese patent publication"), production of methacrolein by oxidation of isobutylene (JP B-41-20693), production of acrylonitrile by ammoxidation of propylene (JP-B-38-19111 and JP-B-38-14717), production of hydrogen cyanide by ammoxidation of methanol (JP-B-54-39839), production of alkenylbenzenes by oxidative dehydrogenation of alkylbenzenes (JP-B-49-41182 and 52-29299), and production of methacrylic acid by oxidative dehydrogenation of isobutyric acid (JP-A-57-134442) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Catalysts used in the above-stated reactions comprise a carrier having supported thereon phosphorus either alone or in combination with other elements. However, they do not always have satisfactory activity and strength. Moreover, preparation of these catalysts involves the problem of poor reproducibility since many of the phosphorus compounds used are easily vaporized due to their relatively high vapor pressure and also they have great effects on accelerating sintering during calcination.
On the other hand, in the preparation of catalyst systems having a high phosphorus content as in the catalyst of the present invention, satisfactory results are not achieved with direct application of conventional processes proposed for preparing antimony-containing catalysts. For instance, the processes disclosed in JP-B-47-18722 (corresponding to U.S. Patent 3,657,155) and JP-B-47-18723 (corresponding to U.S. Pat. No. 3,686,138) are excellent techniques for preparing antimony-containing catalysts suitable for fluidized bed reactions. However, it is difficult to use these processes to produce catalysts containing a relatively large amount of phosphorus while retaining activity and strength sufficient for use in fluidized bed reactions. This is assumed to be because the presence of a large amount of a phosphorus component not only inhibits oxidation of antimony but greatly changes the properties of the slurry which is involved in the processes, thereby reducing its stability.